1. Field of the Invention
The present invention relates to small internal combustion engines, which are used in a variety of applications, such as lawnmowers, lawn and garden tractors, other small working implements such as snow throwers and generators, or in sport vehicles.
2. Description of the Related Art
Small internal combustion engines typically include one or two engine cylinders. Single cylinder engines generally have a valve train of the side valve (“L-head”), overhead cam (“OHC”) or overhead valve (“OHV”) type, and are typically contained within a pair of castings. A first casting may include, for example, the engine cylinder, a portion of the crankcase, and optionally a cylinder head integrally formed with the engine cylinder. A second casting may include a crankcase cover which is attached to the crankcase portion of the first casting to define the enclosed crankcase of the engine. The crankshaft may be disposed in either a horizontal or a vertical orientation, and may be journalled in full bearings, one defined in each crankcase casting, or alternatively, in split bearings, wherein each crankcase casting defines one-half of each of the crankshaft bearings.
Twin cylinder engines generally have valve trains of the overhead cam (“OHC”) or overhead valve (“OHV”) type, and are typically contained within a first casting which includes the engine cylinders and a portion of the crankcase. A second casting typically includes a crankcase cover which is attached to the crankcase portion of the first casting to define the enclosed crankcase of the engine. The crankshaft may be disposed in either a horizontal or a vertical orientation, and may be journalled in full bearings, one defined in each crankcase casting, or alternatively, in split bearings, wherein each crankcase casting defines one-half of each of the crankshaft bearings.
A disadvantage with existing engine designs is that the castings or housing portions which contain known single and twin cylinder engines have a specific construction which is unique to each of the single and twin cylinder engines. For example, a casting which includes a cylinder and a portion of a crankcase of a vertical crankshaft, single cylinder engine can only be used with that particular vertical crankshaft, single cylinder engine. Although certain minor engine components, such as valves, valve springs, carburetors, etc., might possibly be used in a number of different engines, interchangeability of major engine housing components, such as castings or other housing components, between different types of single and/or twin cylinder engines is not possible.
Further, in OHC engines, a camshaft located within the cylinder head of the engine is typically driven with a belt connecting a drive pulley on the crankshaft with a driven pulley on the camshaft. In these engines, assembling the belt to the drive and the driven pulleys can be difficult during the manufacturing process.
What is needed is a small internal combustion engine which is an improvement over the foregoing.